Angular velocity sensor and angular velocity detector

ABSTRACT

The present invention provides a cheap angular velocity sensor capable of detecting angular velocity with high precision by using a vibration mode which cannot be set by external vibration. The angular velocity sensor includes: a vibrator ( 2 ) formed as a solid of revolution and made of a magnetostrictive material; a supporter ( 3 ) disposed on an axis of the vibrator ( 2 ) and supporting the vibrator ( 2 ) at a position where the axis crosses the surface of the vibrator ( 2 ); an excitation coil ( 4 ) for generating a magnetic field along a radial direction around the axis as a center in the vibrator ( 2 ), thereby making the vibrator ( 2 ) vibrate in the radial direction; a detection coil ( 6 ) which is disposed apart from the vibrator ( 2 ) and detects a magnetic flux change caused by a change in the vibration of the vibrator ( 2 ) which occurs depending on angular velocity.

TECHNICAL FIELD

The present invention relates to an angular velocity sensor using avibrator made of a magnetostrictive material and to an angular velocitydetector using the angular velocity sensor.

BACKGROUND ART

To detect angular velocity, various methods are practically usedconventionally. Among them, as an angular velocity sensor which has arelatively simple structure and, moreover, is cheap, there is a widelyused angular velocity sensor employing a method of detecting angularvelocity by detecting, by some method, a Coriolis force generated in thedirection orthogonal to the vibration direction when the angularvelocity is applied to the vibrator in a one-dimensional vibrationalmotion state. The angular velocity sensor is also called a rate gyro. Inparticular, the angular velocity sensor using the vibrator is generallycalled a vibration gyro. In the vibration gyro, in many cases, avibrator is made by using piezoelectric ceramics and, when angularvelocity is applied to the vibrator excited by applying AC voltage, adisplacement which occurs in the vibrator by the Coriolis force isextracted as an electric signal by the piezoelectric effect, and angularvelocity is detected.

However, the piezoelectric angular velocity sensor using thepiezoelectric ceramics has the following problems. Specifically, theangular velocity sensor has to employ either the configuration ofadhering a piezoelectric element to a vibrator or the configuration ofusing a piezoelectric element as the vibrator itself In any of the casesemployed, to drive the piezoelectric element and detect an electricsignal by the piezoelectric effect, a wire has to be connected to anelectrode of the piezoelectric element. As a result, external vibrationis transmitted to the vibrator via the wire, and a problem occurs suchthat the angular velocity cannot be detected accurately.

To solve the problem, for example, in a vibration gyro (10) described inJapanese Patent Laid-open No. Hei 5-1917, as shown in FIG. 1 of thepublication, a vibrator (12) is supported by supporters (22 a and 22 b)attached near a node point. As shown in FIG. 2 in the publication, leadwires (24 a and 24 b) are wound around the supporter 22 b along thevibrator (12). Further, the lead wires (24 a and 24 b) are attached tothe vibrator (12) by an elastic adhesive (26) such as silicone from thesupporter (22 b) to a portion near piezoelectric elements (14 a, 14 b).Similarly, a lead wire (24 c) is partially adhered by the elasticadhesive (26) along the vibrator (12) and is wound around the supporter(22 a). With the configuration, in the vibration gyro (10), the leadwires (24 a to 24 c) are attached to the vibrator (12) by using theelastic adhesive (26), so that the elastic adhesive (26) functions as adumping material. Therefore, external vibration transmitted to the leadwires (24 a to 24 c) is damped (reduced) by the elastic adhesive (2 b)and, as a result, the influence of the external vibration on vendingmode vibration of the vibrator (12) is lessened.

In the vibration gyro (10), however, since the dumping characteristicchanges according to the amount of the elastic adhesive (26), it isdifficult to make the degree of lessening the external vibrationconstant (reproducibility is not excellent). Consequently, a problemexists such that it is difficult to detect the angular velocity withhigh precision. The elastic characteristic of the elastic adhesive (26)changes (deteriorates) due to temperature change or change with time.Therefore, the vibration gyro (10) also has a problem that it isdifficult to excellently reduce leakage of vibration for long period. Itis not easy to manage the elastic adhesive (26) and, moreover,workability of the elastic adhesive (26) is low. There is consequently aproblem that it is also difficult to improve productivity of thevibration gyro (10).

As a method capable of more effectively reducing the influence on thevibrator of external vibration, a vibration gyro in which the vibratoris vibrated in a vibration mode which is hardly set for the vibrator bythe external vibration is proposed. As a vibration gyro of this kind,for example, a gyro (gyroscope) disclosed in Japanese Patent Laid-openNo. Hei 10-267667 is known. In this gyro, a ring-shaped vibrationresonator (1) is suspended in magnetostatic field by a plurality offlexible supporting beams (5), and a vibration mode of vibrating thevibration resonator (1) by electromagnetic induction so that the shapecan be changed from a ring shape to an oval shape or from the oval shapeto the ring shape is used. Since the vibration mode is hardly set byexternal vibration, in the structure, even when external vibration isadded, the influence on the vibration mode is extremely small.Therefore, in the gyro, also in the case where the external vibration isadded, the angular velocity can be detected with high precision.

The gyro has, however, a problem that the plurality of flexiblesupporting beams (5) supporting the vibration resonator (1) have to bemanufactured with high precision by using, for example, micromachining,so that the manufacturing cost is high.

On the other hand, in the angular velocity sensor disclosed in JapanesePatent Laid-open No. Hei 7-20140, excitation generated by a drive coil(12) is given to a vibrator (11) made of a magnetostrictive material,thereby generating vending mode vibration. When angular velocity isadded to the vibrator (11) in the vibration state, the Coriolis force inthe direction orthogonal to the vibration direction is generated in aleg portion of the vibrator (11). In this case, the vibration directionis slightly shifted (twisted) from the basic vibration direction by theCoriolis force. As a result, a stress acting on the leg portion changes,and magnetization caused by an inverse magnetostriction effect alsochanges. Consequently, in the angular velocity sensor, by detecting achange in the magnetization by detection coils (13 a and 13 b), theangular velocity applied to the vibrator (11) can be detected in anon-contact manner.

However, since the vibration mode used in the angular velocity sensor(the vibration mode of making the vibrator (11) vending mode vibrate) isa vibration mode which is easily influenced by external vibration, theangular velocity sensor has a problem such that it is difficult todetect the angular velocity with high precision.

As described above, conventionally, various angular velocity sensorshave been developed. In the angular velocity sensors disclosed inJapanese Patent Laid-open Nos. Hei 5-1917 and Hei 7-20140, since thevibrator is easily influenced by the external vibration, a problem thatit is difficult to detect the angular velocity with high precisionexists. The gyro disclosed in Japanese Patent Laid-open No. Hei10-267667 has a problem such that, although the influence of externalvibration on the vibrator can be reduced, the manufacturing cost is veryhigh.

DISCLOSURE OF THE INVENTION

The present invention has been achieved in consideration of the problemsand an object of the invention is to provide a cheap angular velocitysensor and an angular velocity detector capable of detecting angularvelocity with high precision by using a vibration mode which cannot beset by external vibration.

An angular velocity sensor according to the present invention includes:a vibrator formed as a solid of revolution and made of amagnetostrictive material; a supporter disposed on an axis of thevibrator and supporting the vibrator at a position where the axiscrosses the surface of the vibrator; a magnetic field generator forgenerating a magnetic field along a radial direction around the axis asa center in the vibrator, thereby making the vibrator vibrate in theradial direction; and a detector which is disposed apart from thevibrator and detects a magnetic flux change caused by a change in thevibration of the vibrator which occurs depending on angular velocity.

Preferably, the supporter is made of a magnetic material.

The supporter may include a permanent magnet.

Preferably, an angular velocity sensor according to the inventionfurther includes a case made of a magnetic material for housing thevibrator, the supporter, the magnetic field generator, and the detector.

A first angular velocity detector according to the invention isconfigured by disposing the angular velocity sensor having theabove-described configuration on each of two axes which are orthogonalto each other.

A second angular velocity detector according to the invention isconfigured by disposing the angular velocity sensor having theabove-described configuration on each of three axes which are orthogonalto each other.

As described above, in the angular velocity sensor according to theinvention, the magnetic field generator generates the magnetic fieldalong the radial direction using the axis of the vibrator as a center inthe vibrator, thereby making the vibrator vibrate in the radialdirection, and the detector disposed apart from the vibrator detects amagnetic flux change caused by a vibration change of the vibrator, whichoccurs depending on the angular velocity, thereby enabling the vibratorto be vibrated in a vibration state (vibration mode) which cannot be setin the normal state. Thus, while avoiding inhibition of the vibration ofthe vibrator by the supporter, even when external vibration istransmitted to the vibrator, the vibrator can be maintained in avibrating state in the basic vibrations while hardly influenced by theexternal vibrations. Therefore, the angular velocity sensor can detectangular velocity with high precision also in a state where externalvibration is added. Further, by employing a simple configuration ofsupporting the vibrator only by the supporter, the angular velocitysensor can be manufactured at sufficiently low cost.

In the angular velocity sensor according to the invention, by making thesupporter of the magnetic material, the magnetic field generated by themagnetic field generator can be efficiently supplied to a portion aroundthe axis of the vibrator. Therefore, the vibrator can be vibratedefficiently with low energy.

In the angular velocity sensor according to the invention, the supporteris formed by including a permanent magnet. Consequently, with the simpleconfiguration, the combined magnetic field obtained by adding the DCmagnetic field (bias magnetic field) to the alternating magnetic fieldcan be easily generated in the vibrator. Therefore, a desired magneticfield can be easily generated in each of various vibrators made ofdifferent magnetostrictive materials, so that the vibrator can beefficiently vibrated in a region in which a magnetostriction change islarge and linearity is excellent. As compared with the configuration ofgenerating the combined magnetic field by superimposing DC voltage withalternating voltage, the excitation power can be reduced only by theamount of the DC voltage.

In the angular velocity sensor according to the present invention, byhousing the vibrator, the supporter, the magnetic field generator, andthe detector in the case made of a magnetic material, leakage of themagnetic field generated by the magnetic field generator to the outsideof the case can be prevented, and the influence of the external magneticfield onto the vibrator and the detector can be reduced by suppressinginvasion of the external magnetic fields to the inside of the case.Since the case configures a closed magnetic path for the magnetic fieldgenerated by the magnetic field generator together with the vibrator andthe supporter, leakage magnetic flux can be reduced and, as a result,the vibrator can be vibrated more efficiently.

In an angular velocity detector according to the present invention, bydisposing the angular velocity sensor on each of two or three axes whichare orthogonal to each other, even in a state where external vibrationis applied, the angular velocity in the directions of the two or threeaxes can be detected with high precision.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of an angular velocity sensoraccording to an embodiment of the present invention.

FIG. 2 is an explanatory diagram illustrating an internal structure ofthe angular velocity sensor, an oscillation driving circuit, and asynchronous detector.

FIG. 3 is a plan view of a vibrator and a detection coil indicating thedirection of a magnetic field and the vibration direction in thevibrator in a state where no angular velocity is added to the angularvelocity sensor.

FIG. 4 is a plan view of the vibrator and the detection coil indicatingthe direction of a magnetic field and the vibration direction in thevibrator in a state where clockwise angular velocity is added to theangular velocity sensor.

FIG. 5 is a plan view of the vibrator and the detection coil indicatingthe direction of a magnetic field and the vibration direction in thevibrator in a state where counterclockwise angular velocity is added tothe angular velocity sensor.

FIG. 6 is an exploded perspective view showing the configuration of asupporter including a permanent magnet.

FIG. 7 is an exploded perspective view showing the configuration of anangular velocity detector using three angular velocity sensors.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of an angular velocity sensor and an angularvelocity detector according to the present invention will be describedhereinbelow by referring to the attached drawings.

First, the configuration of an angular velocity sensor according to theinvention will be described with reference to the drawings.

An angular velocity sensor 1 has, as shown in FIGS. 1 and 2, a vibrator2, a supporter 3, an excitation coil 4 as magnetic field generatingmeans, an oscillation driving circuit 5, a detection coil 6 as detectingmeans, a synchronous detector 7, and a case 8. In the embodiment, as anexample, the vibrator 2 is formed in a rotator shape (as an example, aflat disc member) by using a magnetostrictive material having a positivemagnetostriction characteristic which extends irrespective of thedirection of a magnetic field applied. It is assumed that the rotator inthe embodiment is a solid figure formed by rotating a plane figure in aplane around the axis (axis A which will be described later) disposed inthe same plane as a center. As the magnetostrictive material, a materialhaving a positive or negative magnetostriction characteristic,concretely, an Ni-Fe-base magnetostrictive material, an RFe-basemagnetostrictive material, or the like can be used. As themagnetostrictive material, an isotropic magnetostrictive material whosedirection indicative of the magnetostriction effect is random may beused. To increase the efficiency of vibration in the vibrator 2, it ispreferable to use an anisotropic magnetostrictive material whosedirection is aligned with that of a magnetic field applied.

As an example, the supporter 3 is made of a permanent magnet formed in acylindrical shape as shown in FIG. 1. As shown in FIG. 2, the supporter3 is disposed so that its magnetic poles are positioned on the axis A ofthe vibrator 2, and one end side (the upper end side (N pole) in thediagram) is fixed to a portion where the axis A passes in the surface ofthe vibrator 2, that is, in a center portion of the under face of thevibrator 2 in the embodiment to thereby support the vibrator 2. In thiscase, the supporter 3 made of a permanent magnetic always generates amagnetic field having constant intensity in the direction from one endside (N pole) to the other end side (S pole). Therefore, to the vibrator2 in which the upper end side (N pole) of the supporter 3 is fixed tothe center portion of the under face, the magnetic field (bias magneticfield) having constant intensity and extending radially from the centerportion toward the outer periphery is always applied from the supporter3. The magnetic force of the supporter 3 is preset so that the vibrator2 can be biased by the magnetic field of the supporter 3 in a driveregion having excellent linearity. The center portion of the under faceof the vibrator 2 functions as a center point (fixed point) of vibrationby the vibrator 2. The fixed point has the property that even when theangular velocity applied to the angular velocity sensor 1 or thedirection of acceleration changes, the function as the center ofvibration does not change. Therefore, without being influenced byvibration applied from the outside, accurate angular velocity detectioncan be performed in a wide angular velocity area.

As shown in FIGS. 1 and 2, the excitation coil 4 includes a bobbin 11made of a synthetic resin and a coil 12 formed by being wound around thebobbin 11. In this case, the button 11 includes a cylindrical former 11a, a pair of flanges 11 b and 11 c formed at ends of the former 11 a,and a rib 11 d. The bobbin 11 has the function of indirectly supportingthe vibrator 2 via the supporter 3 and directly supporting the detectioncoil 6. Concretely, the former 11 a is configured so that the supporter3 can be inserted from the flange 11 b side to a center hole B in theformer 11 a and the inserted supporter 3 can be held by the innersurface of the former 11 a. As shown in FIG. 2, the former 11 a isconfigured so that its overall length is shorter than the supporter 3and the vibrator 2 attached to the bobbin 11 and the flange 11 b areapart from each other (not in contact with each other). The rib 11 d isformed in a ring shape as an example in the outer peripheral portion ofthe surface facing the vibrator 2 in the flange 11 b so as to be able tosupport the detection coil 6. As shown in the diagram, the rib 11 d isformed so that its inside diameter is larger than the outside diameterof the vibrator 2 and so as not to be in contact with the vibrator 2.With the configuration, the excitation coil 4 is disposed on one of thesides (the lower side in FIGS. 1 and 2) of the vibrator 2 so that itsaxis coincides with the axis A of the vibrator 2. By applying a magneticfield generated by the coil 12 on the basis of a drive signal Sasupplied from the oscillation driving circuit 5 to the vibrator 2 viathe supporter 3, the vibrator 2 is allowed to vibrate. In this case, themagnetic field generated by the coil 12 is alternating magnetic fieldwhose intensity is set to be lower than that of the bias magnetic fieldgenerated by the supporter 3.

As shown in FIG. 2, the oscillation driving circuit 5 generates thedrive signal Sa and a reference signal Sb synchronized with the drivesignal Sa, supplies the drive signal Sa to the coil 12 of the excitationcoil 4, and supplies the reference signal Sb to the synchronous detector7. As an example, the oscillation driving circuit 5 generates AC voltageas the drive signal Sa.

The detection coil 6 has, as an example, a toroidal core 6 a having adiameter which is almost the same as that of the rib 11 d (larger thanthat of the vibrator 2) and a coil 6 b wound around the toroidal core 6a. The axis of the detection coil 6 is coaxial with the axis A of thevibrator 2. The detection coil 6 is disposed around the vibrator 2 withspace from the vibrator 2 so as to be able to detect a change in themagnetic field generated around the outer peripheral surface of thevibrator 2. The synchronous detector 7 synchronous-detects a signal Scinduced at both ends of the coil 6 b by the change in the magnetic fieldgenerated around the outer peripheral surface of the vibrator 2 by usingthe reference signal Sb and outputs a DC detection voltage Vd having avoltage value according to the voltage value of the signal Sc and havingthe polarity (positive or negative) according the phase of the signalSc.

The case 8 has, as shown in FIGS. 1 and 2, an upper case 21 and a lowercase 22 each made of a magnetic material. In this case, the upper case21 is formed in a cylindrical body whose one end (upper end in thediagrams) is closed and the lower end is opened. The inside diameter ofthe upper case 21 is slightly larger than the outside diameter of eachof the excitation coil 4 and the detection coil 6 so that those memberscan be housed in the upper case 21. On the other hand, the lower case 22is formed as a disc member capable of closing the open side (lower endside in the diagram) of the upper case 21, and functions as a cover forthe upper case 21 and a stand on which the supporter 3 for fixing thevibrator 2 and the vibrator 2 are placed. As an example, the lower case22 is formed as a disc member with a step which can be fit in the uppercase 21, and whose center portion in the face on the upper case 21 sideis formed in a cylindrical shape which can be fit in the upper case 21.With the configuration, in a state where the open side of the upper case21 is closed with the lower case 22, a relative positional deviationbetween the upper and lower cases 21 and 22 is prevented. In the case 8having such a configuration, the vibrator 2, supporter 3, excitationcoil 4, and detection coil 6 are housed in a state where their axescoincide with the axis of the case 8. Therefore, the upper and lowercases 21 and 22 made of a magnetic material has the shield function ofpreventing leakage of the magnetic field generated by the excitationcoil 4 to the outside of the case 8 and reducing the influence of theexternal magnetic field on the vibrator 2 and the detection coil 6 bysuppressing invasion to the inside of the case 8 of the externalmagnetic field. The case 8 further has the function of forming a closedmagnetic path for the magnetic field generated by the excitation coil 4together with the vibrator 2 and the supporter 3.

The angular velocity detecting operation of the angular velocity sensor1 will now be described with reference to the FIGS. 2 to 5.

In a state where the drive signal Sa is supplied from the oscillationdriving circuit 5 to the coil 12, the excitation coil 4 generatesalternating magnetic field. The alternating magnetic field is combinedto the bias magnetic field generated by the supporter 3, and a combinedmagnetic field C of the alternating magnetic field and the bias magneticfield is efficiently supplied to the center portion of the vibrator 2via the supporter 3 functioning as a core member to the excitation coil4 (as a magnetic path) as shown in FIG. 2. The combined magnetic fieldsC supplied to the center portion of the vibrator 2 expand radially alongthe radial direction from the center portion to the peripheral portionin the vibrator 2 as shown in FIG. 3, after that, go out from theperipheral surface of the vibrator 2, and pass in the radial directionthrough the toroidal core 6 a. Further, the combined magnetic field Cpasses through the toroidal core 6 a and is absorbed in the upper case21. The combined magnetic field C passes through the upper case 21 andthen the lower case 22 and returns to the supporter 3. In this case,since the combined magnetic field C passes radially from the centerportion to the outer peripheral portion in the vibrator 2, the biasmagnetic field included in the combined magnetic field C expand thediameter of the vibrator 2 as a whole, and the diameter expansion amountchanges in cycles of the alternating magnetic fields included in thecombined magnetic field C. That is, as shown by arrows D in FIG. 3, thevibrator 2 vibrates while repeating expansion and contraction as a wholein the all of directions radially around the axis A as a center. Inother words, the vibrator 2 vibrates around the axis A as a center sothat the outside diameter increases/decreases while maintaining itsplane shape in a circular shape (in FIGS. 3 to 5, the increase/decreaseof the outside diameter of the vibrator 2 is exaggerated, a state inwhich the increase amount of the outside diameter is the maximum isshown by the solid line, and a state in which the increase amount of theoutside diameter is the minimum is indicated by an alternate long andshort dash line). In this case, since the combined magnetic field Cpasses through the toroidal core 6 a in the radial direction, a voltageresulted from the combined magnetic field C is not induced by the coil 6b. As a result, the detection coil 6 does not detect voltage. For easierunderstanding, the vibration directions (the directions indicated by thearrow D in the diagram) along the radial direction around the axis A ofthe vibrator 2 as a center will be also called basic vibrationdirections.

In this state, as shown in FIG. 4, in the case where the angularvelocity in the clockwise direction (the direction of the arrow I in thediagram) around the axis A as a center is applied to the angularvelocity sensor 1, Coriolis force of the magnitude according to theangular velocity is generated in the direction orthogonal to the basicvibration directions D in the vibrator 2, so that the vibrationdirection of the vibrator 2 changes from the basic vibration directionsD to the vibration direction shown by the arrow E in the diagram. Inthis case, the deviation amount between the basic vibration direction Dand the direction of vibration shown by the arrow E changes according tothe angular velocity. Therefore, the direction of the magnetic field(magnetic flux) going out from the outer peripheral surface of thevibrator 2 and going toward the detection coil 6 also changes (shifts)according to the angular velocity in the direction shown by the arrow Fin the diagram (the same direction as the vibration direction E of thevibrator 2). Consequently, the magnetic flux which passes in parallelwith each of the winding wires of the coil 6 b in the detection coil 6at the time of the basic vibration changes so as to cross a plane formedby each of the winding wires. As a result, the signal Sc according tothe angular velocity is induced at both ends of the coil 6 b. Therefore,the voltage value of the DC detection voltage Vd generated by thesynchronous detector 7 also changes according to the angular velocity.

On the other hand, as shown in FIG. 5, in the case where the angularvelocity in the counterclockwise direction (the direction of the arrow Jin the diagram) around the axis A as a center is applied to the angularvelocity sensor 1, the Coriolis force according to the angular velocityis generated in the vibrator 2 in a manner similar to the above, and thevibration direction of the vibrator 2 changes from the basic vibrationdirection D to the vibration direction shown by the arrow G in thediagram. In this case as well, the deviation amount between the basicvibration direction D and the direction of vibration indicated by thearrow G changes according to the angular velocity. Therefore, thedirection of the magnetic field (magnetic flux) going out from the outerperipheral surface of the vibrator 2 and going toward the detection coil6 also changes (shifts) according to the angular velocity in thedirection indicated by the arrow H in the diagram (the same direction asthe vibration direction G in the vibrator 2). Consequently, the magneticflux passing in parallel with each of the wires of the coil 6 b in thedetection coil 6 at the time of the basic vibration changes so as tocross a plane formed by the wires. As a result, the signal Sc accordingto the angular velocity is induced at both ends of the coil 6 b. In thiscase, the polarity (phase) of the signal Sc becomes opposite (reversephase) to that in the case where clockwise angular velocity is appliedaround the axis A as a center to the angular velocity sensor 1.Therefore, the voltage value of the DC detection voltage Vd generated bythe synchronous detector 7 changes according to the angular velocitysimilarly except that the polarity (positive or negative) becomesopposite to that in the case where the clockwise angular velocity isapplied around the axis A as a center to the angular velocity sensor 1.

Thus, by using the angular velocity sensor 1, the direction (clockwiseor counterclockwise direction) of angular velocity applied to theangular velocity sensor 1 can be specified on the basis of the polarityof the DC detection voltage Vd generated by the synchronous detector 7and, on the basis of the magnitude of the voltage value of the DCdetection voltage Vd, the angular velocity can be specified.

As described above, in the angular velocity sensor 1, the vibrator 2 issupported in a state of no contact with other members including thedetection coil 6 by the supporter 3 fixed to the center portion as thefixed point in expansion/contraction vibrations, and the combinedmagnetic field C which radially passes from the center portion to theperipheral portion of the vibrator 2 and whose strength changesperiodically is generated in the vibrator 2 by the supporter 3 and theexcitation coil 4 to make the vibrator 2 vibrate by making the vibrator2 radially expand/contract as a whole in all of directions. By makingthe vibrator 2 vibrate in such a vibration state (vibration mode) whichcannot be set in the normal state, while avoiding inhibition of thevibration of the vibrator 2 by the supporter 3, even when externalvibration is transmitted to the vibrator 2, the external vibration isnot transformed to the vibration mode of the vibrator 2. Consequently,without being influenced by the external vibration, the vibrator 2 canbe maintained in a vibration state in the basic vibration. Therefore,the angular velocity sensor 1 can detect angular velocity with highprecision also in a state where external vibration is applied.

Further, by employing a simple configuration of supporting the vibrator2 by the supporter 3, the angular velocity sensor 1 can be manufacturedat sufficiently low cost. By making the supporter 3 by a permanentmagnet and always applying the bias magnetic field to the vibrator 2 andby making the supporter 3 function as the core for the excitation coil4, the magnetic field generated by the excitation coil 4 can be suppliedefficiently to the center portion in the vibrator 2 (around the axis A).Moreover, the vibrator 2 made of a magnetostrictive material is madevibrate efficiently in a region having high linearity and a large changeamount. Therefore, the vibrator 2 can be efficiently vibrated with lowenergy (small excitation power). Further, by housing the vibrator 2,supporter 3, excitation coil 4, and detection coil 6 in the case 8 madeof a magnetic material, leakage of the magnetic field generated by theexcitation coil 4 to the outside of the case 8 can be prevented, and theinfluence of the external magnetic field onto the vibrator 2 and thedetection coil 6 can be reduced by suppressing invasion of the externalmagnetic fields to the inside of the case 8. Since the case 8 configuresa closed magnetic path for the magnetic field generated by theexcitation coil 4 together with the vibrator 2 and the supporter 3,leakage magnetic flux can be reduced and, as a result, the vibrator 2can be vibrated more efficiently.

The present invention is not limited to the foregoing embodiment. Forexample, the case of forming the supporter 3 by a permanent magnet andmaking the vibrator 2 vibrate by the combined magnetic field C by usingthe AC voltage as the drive signal Sa has been described in theforegoing embodiment. Alternately, the supporter 3 may be formed by amagnetic body which is not magnetized. In this case, the bias magneticfield applied to the vibrator 2 by forming the supporter 3 by apermanent magnet is generated by the excitation coil 4 by using DCvoltage superimposed with the drive signal Sa. With the configuration,although the circuit configuration of the oscillation driving circuit 5becomes slightly complicated and power (excitation power) consumed bythe oscillation driving circuit 5 and the excitation coil 4 increasesonly by the amount corresponding to the DC voltage superimposed, in amanner similar to the foregoing embodiment, the vibrator 2 can bevibrated efficiently in the region having excellent linearity and alarge change amount. Alternately, the configuration of forming thesupporter 3 by a magnetic body which is not magnetized and supplyingalternating voltage to which the DC voltage is not superimposed as thedrive signal Sa to the excitation coil 4 can be employed. With theconfiguration, although the oscillation driving circuit 5 can beprevented from becoming complicated since the DC voltage is notsuperimposed with the drive signal Sa, since the bias magnetic field isnot applied to the vibrator 2, the efficiency of vibrating the vibrator2 deteriorates. However, the simple magnetic body can be used as thesupporter 3 and the oscillation driving circuit 5 can be configuredsimply. Thus, the angular velocity sensor 1 can be configured simply andcheaply. Further, the vibrator 2 can be made vibrate at a frequencytwice as high as that in the configuration in which a bias magneticfield is applied. Thus, the angular velocity sensor of high vibrationfrequency can be simply configured.

On the other hand, the supporter 3 can be also formed by including apermanent magnet in part of it. In other words, the supporter 3 can bealso formed by combining the magnetic body which is not magnetized and apermanent magnet. With the configuration, only by replacing thepermanent magnet, the strength of the DC magnetic field can be easilychanged. Consequently, angular velocity sensors of variouscharacteristics can be manufactured easily. For example, as shown inFIG. 6, the supporter 3 can be also formed by inserting a metal magnet(permanent magnet) 3 b having a circular column shape into a center hole3 h of a ferrite material (cylindrical magnetic body which is notmagnetized) 3 a having a cylindrical shape. With the configuration, byusing the cylindrical ferrite material 3 a as a common part andpreparing the metal magnets 3 b having various magnetic characteristicsas the metal magnet 3 b to be inserted in the center hole 3 h, thecharacteristic of the angular velocity sensor 1 can be easily changed.Since the metal magnet 3 b can be easily fit in the ferrite material 3a, the supporter 3 can be manufactured easily. When the supporter 3 isnot used as a core member for the excitation coil 4, the supporter 3 canbe made of a nonmagnetic material (for example, synthetic resinmaterial). In the case where the supporter 3 is made of a nonmagneticmaterial, in place of the configuration of disposing the supporter 3below the vibrator 2 to support the vibrator 2, a configuration ofsupporting the vibrator 2 in a suspended state by disposing thesupporter 3 coaxially with the axis A between the center portion in thetop face of the vibrator 2 and the case 8, fixing the upper end side tothe case 8, and fixing the lower end side to the center portion in thetop face of the vibrator 2 can be also employed. In this case, it ispreferable to dispose the magnetic body as a core member in the former11 a of the excitation coil 4. With the configuration, in a mannersimilar to the foregoing embodiment, the magnetic field generated by theexcitation coil 4 via the magnetic body can be efficiently supplied tothe center portion of the vibrator 2. In this case, it is preferable tomaintain the contact state between the magnetic body and the vibrator 2.It is not always necessary to make the magnetic body and the vibrator 2come in contact with each other. The configuration in which a gap isinterposed between the magnetic body and the vibrator 2 can be alsoemployed. Further, a configuration of fixing supporters 3 to the top andunder faces of the vibrator 2 and supporting the vibrator 2 by the pairof supporters 3 may be also employed. In this case, the supporter 3disposed on the side opposite to the excitation coil 4 over the vibrator2 is made of a nonmagnetic material.

Although the case where the vibrator 2 is formed as a disc member hasbeen described in the foregoing embodiment, the shape of the vibrator 2may be a rotator. Other than the disc member, for example, a sphericalshape, a circular column shape (solid thicker than the disc member), aconical shape, a truncated cone shape, or a solid shape obtained bycombining any of the shapes may be also employed. Similarly, thedetection coil 6 is not limited to the ring shape but may be configuredby disposing one or more circular arc members. The detection coil 6 maybe also configured only by the coil 6 b, that is, an air core coil.Further, in place of the detection coil, a semiconductor magnetic sensorusing the Hall effect or magnetoresistive effect can be also used. Thevibrator 2 can be also formed by using, in place of a positivemagnetostrictive material, a negative magnetostrictive material whichshrinks irrespective of the direction of a magnetic field applied.

The angular velocity sensor 1 can be used singly. As shown in FIG. 7, athree-axis angular velocity detector 31 can be also configured bycombining three angular velocity sensors 1A, 1B, and 1C. The angularvelocity detector 31 includes the three angular velocity sensors 1A, 1B,and 1C, a fixing member 32, and the oscillation driving circuits 5 andthe synchronous detectors 7 (which are not shown) for the angularvelocity sensors 1A, 1B, and 1C. In this case, the angular velocitysensor 1A is set so that its axis is in parallel with the X axis, theangular velocity sensor 1B is set so that its axis is in parallel withthe Y axis, and the angular velocity sensor 1C is set so that its axisis in parallel with the Z axis. The angular velocity sensors 1A, 1B, and1C are fixed to the fixing member 32. The angular velocity detector 31can detect angular velocity in all of the three axes simultaneously.Although not shown, in the case of detecting the angular velocity addedto an object which moves only in a predetermined plane, for example, atwo-axis angular velocity detector can be also configured by the twoangular velocity sensors 1A and 1B without using the angular velocitysensor 1C disposed in the Z axis in the diagram.

In the angular velocity sensor 1, the supporter 3 may be made of amagnetostrictive material. Obviously, the angular velocity sensor 1 andthe angular velocity detector can be applied not only to a camera-shakecorrecting mechanism (unsteadiness correcting mechanism) employed for avideo camera or the like but also to a navigation system and an attitudecontroller of a car, an airplane, or the like.

1. An angular velocity sensor comprising: a vibrator formed as a solidof revolution and made of a magnetostrictive material; a supporterdisposed on an axis of the vibrator and supporting the vibrator at aposition where the axis crosses the surface of the vibrator; a magneticfield generator for generating a magnetic field along a radial directionaround the axis as a center in the vibrator, thereby making the vibratorvibrate in the radial direction; and a detector which is disposed apartfrom the vibrator and detects a magnetic flux change caused by a changein the vibration of the vibrator, the change in the vibration occurringdepending on angular velocity.
 2. An angular velocity sensor accordingto claim 1, wherein the supporter is made of a magnetic material.
 3. Anangular velocity sensor according to claim 2, wherein the supporterincludes a permanent magnet.
 4. An angular velocity sensor according toclaim 1, further comprising a case made of a magnetic material forhousing the vibrator, the supporter, the magnetic field generator, andthe detector.
 5. An angular velocity detector configured by disposing anangular velocity sensor on each of two axes which are orthogonal to eachother, wherein each of the angular velocity sensors comprises: avibrator formed as a solid of revolution and made of a magnetostrictivematerial; a supporter disposed on an axis of the vibrator and supportingthe vibrator at a position where the axis crosses the surface of thevibrator; a magnetic field generator for generating a magnetic fieldalong a radial direction around the axis as a center in the vibrator,thereby making the vibrator vibrate in the radial direction; and adetector which is disposed apart from the vibrator and detects amagnetic flux change caused by a change in the vibration of thevibrator, the change in the vibration occurring depending on angularvelocity.
 6. An angular velocity detector configured by disposing anangular velocity sensor on each of three axes which are orthogonal toeach other, wherein each of the angular velocity sensors comprises: avibrator formed as a solid of revolution and made of a magnetostrictivematerial; a supporter disposed on an axis of the vibrator and supportingthe vibrator at a position where the axis crosses the surface of thevibrator; a magnetic field generator for generating a magnetic fieldalong a radial direction around the axis as a center in the vibrator,thereby making the vibrator vibrate in the radial direction; and adetector which is disposed apart from the vibrator and detects amagnetic flux change caused by a change in the vibration of thevibrator, the change in the vibration occurring depending on angularvelocity.